The present invention relates to a method and an apparatus for treating exhaust gas.
In general, exhaust gas exhausted from a fossil fuel fired boiler installed in a thermal power plant contains sulfur oxides, such as sulfur trioxide (SO3) as well as sulfur dioxide (SO2). However, if SO3 contained in exhaust gas becomes fumes, the fumes of SO3 may form a mist of H2SO4, which is hazardous with a strong corrosive nature. The mist of H2SO4 consists of submicron particles that substantially cannot be collected by a mere gas-liquid contact with an absorbent. Accordingly, in order to prevent the corrosion of the apparatus and to achieve cleaner exhaust gas, it is necessary to carry out processing to remove SO3 from exhaust gas.
JP 63-175653 A discusses a method for controlling the amount of dust to be collected according to an estimated value of the SO3 concentration contained in exhaust gas at an inlet of an electrostatic precipitator, which is calculated according to a result of measurement of the SO2 concentration at an inlet of a desulfurization apparatus, so that a ratio between the SO3 concentration and the dust concentration at the outlet of the electrostatic precipitator becomes a predetermined value in order to maintain a low corrosion amount in a gas to gas heater (GGH).